Space-Time Channel Shortening Based Spatial Multiplexing Schemes for Multiusers with Multipath Channels

We provide a spatial multiplexing scheme for multiusers with multipath channels. The proposed technique is based on extension of uplink-downlink duality previously known for flat fading channels. We first demonstrate that the key result of the uplink-downlink duality that both links share the same signal to interference plus noise ratio and normalized MSE regions under sum power constraint holds for multipath channels as well. We then propose spatial multiplexing schemes based on space-time pre-equalization and space-time pre-channel shortening and demonstrate that the pre-channel shortening at the transmitter has the ability to reduce substantially the required total transmitter power for a given set of multi-user SINR targets. The results are fully supported by Monte-Carlo simulation results.